Chapter 5 Scottish mineral Geological Conservation Review sites – Hydrothermal veins and mineral assemblages

Abstract

This fifth paper on Scottish mineral Geological Conservation Review (GCR) sites details those of highest conservation value for hydrothermal veins and associated mineral assemblages. The GCR sites are both large and small reflecting variations in past economic mining and extraction history. During the long mining histories, and after, the sites have yielded new mineral species and a new metal. From the largest ore field for lead, zinc and copper 80 or so minerals have been recognised, including nine new species, one of which was established as the first sulphite, scotlandite. Elsewhere gold and silver were also extracted. For some veins the country rocks were analysed to determine whether they provided the vein elements for primary and secondary minerals, and sometimes dated. Two sites exhibit polymetallic mineralisation, i.e., five elements in the mineral assemblages. In one site veins in close proximity to a sanukitoid pluton received signature elements from the intrusion. Veins in various areas formed in faults, fractures and shears which became conduits for ground waters reacting with vein minerals. Oxygen in the water reacted with lead, zinc and copper minerals and in the presence of CO2 and SO4 supergene mineral assemblages formed in appropriate alkalinities. It is therefore possible to establish paragenetic sequences and calculate stability fields for specific assemblages. Alkalinities and formation temperatures may also be obtained through fluid inclusions studies and isotope analysis.